1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to an ink sensor for an ink jet printer.
2. Description of the Related Art
Occasionally, under error conditions such as a paper jam or the like, an ink jet printer may print on the platen. Another cause of printing on the platen is using paper that is too narrow for the print job. This is a very detrimental situation, because the ink on the platen becomes very gummy, and contributes to future paper jams, ink smear on the back side of subsequent pages, degraded roller performance, head-to-paper gap problems, etc.
The presence of paper is generally sensed when it enters the nip of the pinch roller just before the paper enters the print zone. Sometimes, paper will jam at this point, such that the printer senses paper present, but no paper is actually in the print zone. Presently, ink jet printers do not have a means to detect that ink is then printing on the platen.
What is needed in the art is a simple, low-cost device for sensing the jetting of ink droplets within an ink jet printer.
Present-day ink jet printers with disposable printheads often continue to function even when the printhead cartridge or bottle has been depleted of ink. This is because they do not have a means to accurately monitor ink usage and accurately detect when ink is depleted. This requires that a user rerun a job if the ink has run dry during his job. For a long job this a severe nuisance.
Many schemes exist in the prior art to sense ink out. These schemes meet with varying degrees of functionality and accuracy. One example is a dot-counting scheme wherein ink usage and an xe2x80x9cink-outxe2x80x9d point is estimated based on the dot count. Another scheme uses an optical sensor and a clear ink bottle to xe2x80x9cviewxe2x80x9d the ink level in a special cavity of the bottle. Another method relies on the back pressure of a collapsed lung internal to the bottle. There are also capacitive, resistive, carrier mass measurement and many other types of sensing ink level. Among the disadvantages of the prior art sensors are that they are expensive, they are inaccurate, or they disable the printhead with an amount of ink still in the head.
What is needed in the art is a simple, low-cost, accurate device for sensing when an inkjet printhead has run dry.
There is an optimal operating point for ink jet printheads such that when they are operated at too low a supply voltage they do not jet, but when they are operated at too high a supply voltage they will suffer reduced life. Optimally, it is desired to operate the printhead at voltage just above that required to begin jetting the nozzles, i.e., the point of nucleation. Ideally, it is desired to automatically detect this point for an individual printer, as this voltage varies from printer to printer due to component tolerances, environmental factors, etc. Thus autonucleation detection is a desired function for an inkjet printer.
Schemes exist in the prior art to detect printhead nucleation voltage. One example is a printhead temperature sensing scheme wherein the voltage is stepped up repeatedly, and the printhead temperature is monitored. The temperature increases with the voltage until nucleation, after which there is a detectable fall in temperature for a given fire voltage because energy and therefore heat is being carried away from the head with the fired ink droplets. Thus, the nucleation voltage is inferred from the inflection point of a plot of temperature versus voltage.
A second scheme involves setting a voltage, printing a pattern on a page, and sensing with an optical sensor whether the pattern actually printed. If not, the voltage is stepped up, the pattern is printed, optical sensing is performed, etc, and this process is repeated until the printed pattern is sensed, indicating that the nucleation voltage has been reached.
Among the disadvantages of the prior art schemes are that they are generally expensive and complex, requiring optical or temperature sensing, and perhaps requiring printing of a test page, etc. Also, the determination of the inflection point of the temperature versus voltage plot is prone to inaccuracies, as the inflection is a subtle one and the system is prone to noise.
What is needed in the art is a simple, low-cost, accurate device for detecting autonucleation.
The present invention provides a simple, low-cost sensor apparatus that can detect whether ink droplets are being jetted within an ink jet printer, and whether the ink drops are being jetted in a certain area of the printer, such as on the platen.
The present invention also provides a device for sensing when an inkjet printhead has run dry, and pausing a job at the page on which the head runs dry, and allowing the user to replace the head cartridge. The job is then resumed such that the driver reruns the last page and completes the job.
The present invention further provides a low-cost, simple device that can detect when autonucleation has taken place in an ink jet printer.
The invention comprises, in one form thereof, an ink detection sensor for an ink jet printer. Two terminals define a substantially linear gap therebetween. An ink support device supports ink in the gap between the terminals. An electrical measuring device detects a change in an electrical resistance between the terminals when ink is supported in the gap by the ink support device.
The invention comprises, in another form thereof, a method of operating an ink jet printer, including monitoring whether ink is impinging upon a platen of the ink jet printer. A print job is stopped if it is detected that ink is impinging upon the platen.
An advantage of the present invention is that it can be determined whether ink is being jetted onto a platen of an ink jet printer.
Another advantage is that the cost of the sensor is much less than that of a reflective, optical type sensor. The sensing circuit requires just a few low cost components.
Yet another advantage is that no special alignment of the sensor in the printer is required. This allows ease of printer manufacturing assembly.
A further advantage is that it can be determined whether an ink jet printer is out of ink.
A still further advantage is that autonucleation of ink within an ink jet printer can be detected.